Pulse operated system



B. M. OLIVER PULSE OPERATED 4SYSTEM original Filed Feb. g4, y1944 4 "Sheets-Sheet l /NVE/VTO? M. 0L VER s, MM?

ATTORNEY B. M. OLIVER PULSE OPERATED SYSTEM 4 Sheets-Sheet 2 Original Filed Feb. 24, 1944 a gu NN ...ooo'

/N Vas/ron BM OL/ VER ATTRNEV.

` B. M. OLIVER rULsE OPERATED SYSTEM 4 Sheets-Sheet 3 Original Filed Feb. 24, 1944 ATTORNEY R Mw. .MU ww B M vr B vom@ Original Filed Feb. 24, .1944

B. M. OLIVER PULSE OPERATED SYSTEM 4 Sheets-Sheet 4 TRANSM/ T TED RANGE u/v/r PuLsE RANGE SE TT/NG FIG.4

Y2-ur oFF L INE CURRENT rHRoc/cH me Two HAL vEs QF aloof w auf ro l aA r/Nc mal/Es ALONE.

,0o/U ECHO'B I Emo/SI x I A Isc/10% /v/afo s/cNAL /07 /07 Elf-H0 107 /07 r 400 YD.

oL-LAY I ELEcrL-D I -0 CUTOFFLINE' SWPRESSED OUTPUT GE @I0 I(.C.GATING WAVES GENER TUR SH/F TED 90 CURRENT THROUGH TWO HALVE S OF T UEE' V8 DUE T0 GA T/NG Wl/ES ALONE-[N117: l. C. CIRCUIT CURRENT THROUUH RIGHT HALF 0F TUBE V6 WHENSELECTED ECHO /09 IS WITH/N MIDDLE 200 YDS. 0F PULSE [08.

TUBE V6 WHENSELECTED ECI-I6 [09 j g2 THIN MIDDLE 200 YDS. 0F

I CURRENT W'IROUGHLEFTHALFOF loe IN VE IV TOR .M OLII/ER ATTORNEY Patented Oct. 4, 1949 PULSE OPERATED SYSTEIW Bernard M. Oliver, New York, N. Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York s Original application February 24, 1944, Serial No.

Divided and this application March 19, 1945, Serial No. 583,471

Thisinvention relates to switching circuit arrangements and more specifically to arrange-f ments `of this character controlled by pulses. This application is a division of application, Serial No. 523,721, filed February 24, 1944.

It is` an object of this invention to provide a novel switching circuit arrangement operated by pulses.

It is another object of this invention to provide a novel system including a circuit element, two means for applying energy thereto, and pu1se. controlled means for selectively connecting said energy applying means to said circuit element.

It is still another object of this invention to provide a circuit arrangement responsive to the failure of, or unexpected change in position or spacing of, a series of normally received time spaced pulses for switching a circuit element from one energy applying means to another. I

An illustrative embodiment of the switching circuit of this invention and one of its applications will be described below in connection with an automate tracking radar system wherein it is y desired to switch from automatic to manual tracking upon the failure of normally received incoming pulses or when for any reason the ncoming echo pulses arrive at such an advanced or retarded time or are in any way modified so that the automatic handling of them for automatic tracking would fail or become ineicient, butit is obvious that the switching circuit arrangement of this invention has much broader application and, hence, it is not limited in use to `radar' systems.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which:

Fig. 1 is a schematic block diagram of 'a radar system employing a pulse-operated switching circuit arrangement in accordance with the invention;

Fig. 2 is a circuit diagram of a portion of the automatic range tracking unit forming part lof the system of Fig. 1; y

Fig. 3 is a circuit diagram, partly schematic, of the automatic tracking indicator and control circuit forming part of the system of Fig. 1; and

Figs. 4 and 5 are diagrammatical and graphical representations to aid in understanding the invention. f

Referring more particularly to the drawings, Fig. 1 is a single -line block diagram to show the relationship of the various elements of a radar system utilizing a switching circuit arrangement 2 claims. (ci. 31a-44o) in accordance with the invention. In the ar rangement of Fig. 1, an ultira-high frequency pulse modulated wave is produced in the the transmitter I0. 'I'he transmitter may comprise, for example, a high voltage rectifier of any suitable form which supplies about 12,000 volts direct current to a suitable charging circuit or element capable of producing a still higher voltage. After the charging voltage builds up to about 21,000 volts, any suitable rotary spark gap discharges the capacitor in the charging circuit. This discharge takes place in about 1 microsecond and causes a magnetron 'oscillator in the transmitter to oscillate for this brief period and send short pulses of radio frequency energy through a T-R box II to an antenna I2 which, for example, includes a waveguide and a parabolic reflector. Any suitable antenna may be used. Radiations from the antenna strike one or more objects and produce reflections or echoes therefrom which are received by the antenna I2 and transmitted through the T-R box II to the receiver I3. The T-R box can be 'of any desirable type, for example, that employing a Western Electric Company '709-A tube in a resonant cavity. This tube is filled with an ionizable gas and has a small gap therein. During reception of the low voltages of the received energy the gas is not ionized, the

cavity is tuned to resonance and the received energy is applied to the receiver I3. During the emission of a transmitted pulse from the transmitter I0, the voltage due to the pulse ionizes the gas thus detuning the cavity and substantially preventing the energy of the pulse from reaching the receiver I3.

In the receiver I3 the received waves are heterodyned to a convenient intermediate frequency and those intermediate frequency waves are amplified, detected, and applied to the signal selector 20 in the automatic range tracking unit I4. The unit I4 will be described more fully below.

-Pulse energy from the transmitter III, which is in the nature -of a synchronizing pulse, controls the range unit I5 'which is essentially a variable delay circuit or unit which produces a pulse IOI of predetermined length a controllable period of time Iafter fthe initiation of the pulse from the transmitter I0 (which is in the same position as, or slightly before or slightly after, the pulse |00 in Fig. L1--A). A suitable range unit is disclosed in an Aapplication of L. A. Meacham, Serial No. 491,791, led June 22, 1943, `$16. which issued on June 1'7, 1947, as Patent 2,422,204, or in an article entitled The SCR-584 Radar in the February 1946 issue of E1ectronics, beginning on page being initiated after a time interval correspond-.

ing to a range of 400 yards :from the start of the pulse from the range unit I5. A suitable circuit to perform the functions of the unit 2| is disclosed in a copending application of B. M. Oliver, Serial No. 523,722, iiled February 24, 1944 which issued on Oct. 19, 1948, as Patent 2,451,632, or in Patent 2,226,706, issued December 31, 1940, to M. Cawein. The output pulse |08 from the delay circuit and pulse generator 2| (see Fig. 4-G) is also fed to the signal selector 20. A suitable signal selector is a vacuum tube circuit which acts as a gate to permit only those signals which occur within the duration of the pulse |08 to be passed on to the range detector 25. Such a selector is shown in the above-mentioned Oliver patent.

The output pulse IOI from the range unit I is also applied to a pulse generator 22 which produces a negative or notch pulse |02 (shown in Fig. 4--C) which is applied to the gating waves generator 23. The pulse |02 has a time duration c-orresponding to 1200 yards range, for example, and ythis pulse is started by the range unit pulse I0|. Fig. 4-D shows two gating waves |03 and |04 which are produced by the generator 23. The waves |03 and |04 are applied to a range vdetector 25 to which is also applied the selected portion of the video signal from the signal selector 20. This selected signal is represented by .the pulse |09 in Fig. 4-H 'and is produced by applying a wave such as that shown in Fig. 4-F (representing received and detected pulse |00 corresponding t-o the transmitted pulse, various echoes |01 and noise voltage components) to the input circuit of the signal selector 20 along with 'rthe G-yard position or pedestal puise |08. 'Ihe pulse |08 acts as a gate to cause the signal selector 20 to pass current for the duration of this pulse and reject all portions of the signal produced by the receiver I3 which do not occur within the time span of the 40G-yard pulse |08. This is represented in Fig. 4H, the selected echo signal being shown by the pulse |09. In other words, the signal selector 20 has an output current only during the time span of the pulse 08 and the position of this pulse with respect to the pulse |00 is determined by the position of the range lunit pulse IOI with respect to the pulse I 00. The range detector 25 which will be more fully described below in connection with Fig. 2 comprises two diodes to the plates of which are -applied respectively the gating waves |03 and |04 from the amplifier 24 and to the plates of both of which is applied the selected signal from the circuit 20. Integrating condensers are connected to the cathodes of the diodes and voltages are produced thereacross which are respectively representative of the total current passed by the diodes during the positive halves of the waves |03 Iand |04 by means which will be described below. If the pulse |09 is n-ot symmetrically positioned in time with respect to the gating waves |03 and |04 (it has been shown as being symmetrically positioned with respect to the middle positive pulses of the waves |03 and |04) a diiferential current is produced which is utilized to drive a motor 28 to control the range unit I5 in such a way Ias to vary .the position of the range unit pulse IOI shown in Fig. 4-B with respect to the pulse |00 shown in Fig. 4-A. The current used to drive the motor 4 20 is produced in the modulator 28 to which th signal current from the range detector 25 is applied in addition to 60-cycle waves from the source 35 acting through a phase shifter 29. The output of the modulator 26 which is a 60-cycle wave amplitude-modulated by the signals from the circui-t 28 is amplified in the amplifier 21 and applied to the motor 28 through an amplifier 30, contact 3|, and armature 33 of the control rel-ay 34 which latter is operated by means of the automatic tracking indicator and control circuit I6 to be described more fully below.

Before describing in detail the circuit I6, a more detailed description of the automatic range tracking unit I4 with reference to Fig. 2 will be given. Fig. 2 shows the pulse generator 2'2, the 410ki1ocycle generator 23 of the two gating waves, amplifier 24, range detector 25 and direct coupled amplier 25A. The pulse generator 22 comprises a tube VI to the control grid of which is applied through a resistor 40 the positive pulses |0| (one for each transmitted pulse" |00) from the range unit l5. 'I'he cathode of this tube is connected to the suppressor grid and also to ground through the parallel connected condenser 4| and resistor 42. The cathode is also connected through resistors 43 and 44 to the positive terminal of a source 45 of constant potential of 300 volts, for example. While the source 45 has been represented schematically as a battery, the negative terminal of which is connected to ground, it is to be understood that any other suitable source can be used. The screen grid of the tube VI is connected through the resistor 44 to the positive terminal of the source 45 and through a condenser 46 to ground. The plate of the tube VI is connected through the resistor 4'!v to the positive terminal of the source 45 and through a condenser 48 and a resistor 49 to the grid of the tube V2 in the generator 23. Connected between the common terminal of the condenser 48 and4 the resistor 49 and ground is a tuned circuit T comprising a parallel connected inductive member 50 and condenser 5I, the latter preferably being adjustable and only a few micromicrofarads. The control grid of the tube VI is biased below cut-oft by placing the cathod at a positive potential by means of the resistors 42, 43 and 44, these resistors acting as a voltage dividing potentiometer.` When the range unit pulse |0| is applied to -the grid of the tube Vl, this tube conducts plate current for the instant that the control grid is above the cut-off voltage. The pulse of plate current drawn by VI during the time of the range unit pulse |0I charges the condenser 5I through the path comprising this condenser, the condenser 48, the plate-cathode resistance of VI, and the condenser 4|. This causes the plate voltage to drop about 200 volts and since condenser 48 is much larger than condenser 5|, the grid of the tube V2 is driven negative by the same amount. The LC networli comprising the members 50 and 5I begins an oscillation which is quenched after one-quarter cycle because the voltage across -it begins to swing positive and the grid of tube V2 begins to draw current. The volt' oscillation of the network T and produces, by means of apparatus now to be described. plate -voltage waves |03 and |04 shown in Fig. 4-D.

vsecondary winding 55. The primary winding 54 is shunted by a condenser 56 and the mid-point of the winding 54 is connected to the cathode of tube V3, the mid-point of the winding 55 being' connected to ground. The winding 54 has one of its terminals connected to the plate of the tube V2 and through a condenser 51 and resistor 58 to the control grid of the tube V3. The winding 54 has its other terminal connected through the resistor 59 to the positive terminal of the direct current source 45 and through a condenser 60 to ground. The terminals of the secondary winding 55 of the-transformer 53 are connectedfto any suitable push-pull amplifier 24. VThe cathode of the tube V2 is connected to ground and the cathode of the tube V3 is connected through the resistor 6| to ground. A grid leak resistor 62 is connected in the grid-cathode circuit of the tube V3 while the plate of the tube V3 is connected through the resistor 63 to the upper terminal of the Winding 54.

The grid of the tube V2 receives the 1200-yard negative pulse |02 from the tube VI. Plate current for the tube V2 normally ilows through the transformer winding 54 in` the network 52. The voltage pulse |02 applied to the grid of the tube V2 cuts the tube off and the change in plate eurrent of V2 causes the tuned circuit of the network 52 yto oscillate. When the grid voltage of the tube V2 rises above cut-off (after a period of time corresponding to a range of 1200 yards), plate current ilows again through V2, and the low plate resistance of this tube damps out the oscillations.

The tube V3 is used to supply feedback to the network 52 `of just the' proper amount to make up for its losses and thereby maintain a constant amplitude for all cycles in the oscillation. The condenser 5| is adjusted until the duration of the large negative grid voltage wave |02 extending below cut-oli of the tube V2 is just long enough to produce three complete oscillation cycles of the network 52 before the oscillations are damped out. The wave forms of these oscillatory waves |03 and |04 are shown in Fig. 4-D.

The voltage waves |03 and I 04 produced at the respective terminals of the secondary transformer winding 55 are amplified by any suitable push-pull amplifier 24 and applied respectively to the two plates of the double diode tube V4. Equal resistors 64 and 65 are connected in series across the output terminals of the push-pull amplier 24 and the common terminal of these two resistors is connected through a resistor B6 to ground. The left cathode of the tube V4 is connected through the parallel-connected resistor 61. and condenser 68 and the resistor 69 to ground, while the right cathode of the tube V4 is connected through the parallel-connected resistor 10 and condenser 1| and the resistor v69 to ground. The two cathodes are also connected through the series resistors 12 and 13, respectively, to the input terminals of the direct coupled amplifier A which is of any Sula able form. Equal condensers 14 and 15 are connected across the input terminals of the ampliiler 25A, the common terminal of the two condensers" being connected to ground. 'The elements 12 andl 14 and 13 and 15 serve as two low-pass iilters.

The action of the range detector is as follows:

The amplified output waves of the 410-kilocyclethe two plates of the double diode tube V4. A

coupling condenser 16 can be used in this input circuit if desired. The period of the selected signal shown in Fig. 4H is, as pointed out above and as shown in Fig. 4, of the proper length of time to correspond to 400 yards range and this G-yard pulse coincides\with the time of the middle cycle of the two 410-kilocycle sine wave oscillations. Once this adjustment is made, .the relation between the 40o-yard pulse shown in Fig. 4-G with respect tothe waves shown in Fig. 4-D remains xed even though the time of occurrence of all of these`may vary with respect to the time of occurrence of the corresponding transmitted pulse |00, this variation being caused by the changes in time of occurrence of the range unit pulse |0| when the apparatus is being utilized to track the selected target.

If no signal is applied to the plates of the tube V4 lfrom the signal selector 20, the currents through the vtwo halves'of the double diode V4 will be equal and will appear as two series of positive half sine waves |05 and |06, Fig. 4-E, as each half of the tube V4 conducts alternately. The pulses are integrated by the condensers 68 and 1I'. The resulting signal voltages 'are applied to the two grids of a balanced direct current amplier arrangement represented schematically by the box 25A in Fig. 2 through the lters 12, 14 and 13, 15 and in turn produce equal voltages.

If there is a signal exactly in the center of the 40G-yard pulse shown in Fig. 4.G, its voltage will add equally to the voltage appliedto the two sections of the tube V4 to cause increased currents to flow. The currents through the two halves of the double diode V4 will be increased by the same amount so that the two currents will still be equal. As before, this will result in equal signal voltages at the input of the modulator 26.

If the selected echo signal |09 occurs in the rst 200 yards of the 400yard range pulse, one-half of tube V4, say, for example, the right half, will be conducting. The positive voltage of the video l signal will add to the voltage on this plate to cause an increase in the ow of current through this diode. The voltage applied to the left plate of the tube V4 will be negative at this instant and the selected signal cannot cause current to ow in this half of the tube. A half cycle later the left plate will be positive and cause current to flow but the signal will not be present to add to this current so that it will be less than that which iiowed in the right half.

If the signal from 'the target occurs in the second 200 yardsv of the 40G-yard range pulse |08,A

the current flow through the resistor 61 will be increased While the current flow through the resistor I8 will remain normal. The eIl'ect is the reverse of that which takes place under the conditions described in the immediately preceding paragraph. The unequal voltages to ground at these resistors are applied to the input circuits of the balanced direct coupled amplifier 25A and then applied to the modulator 26.

The modulator 26 preferably comprises a bridge structure of four rectifier elements such as that shown in F. A. Cowan Patent 2,025,158 issued December 24, 1935. An alternating current from a suitable source, such as the source of 60-cycle voltage 35. is applied through a 90-degree phase shifting network 29 to one diagonal of the bridge, the other diagonal being connected to the output terminals of the direct coupled amplifier 25A. The modulator 26 operates in accordance with the description in the Cowan patent to suppress the carrier from the source 35 and transmit to the output circuit of the modulator substantially only the upper and lower sidebands produced by the amplitude modulation of this carrier by the signal input The output wave from the modulator, comprising a (iO-cycle, signal-modulated wave, is amplified by the amplifier 21 which may be of the conventional push-pull type and by a second amplifier 38 of any suitable type, one of the output terminals of this latter amplifier being connected to the contacts 3| of the control relay 36. When the control relay 34, in a manner to be described more fully below, is operated to the automatic position, the amplifier 38 is connected through the contact 3| and armature 32 of the control relay 34 to a suitable motor 28 which is preferably of the two-phase low inertia type. The output of the amplier is applied to one of the two eld windings of the two-phase motor and an unmodulated 60-cycle voltage is applied to the second field winding of the motor 28 from the source 35. Since the carrier input to the modulator 26 is shifted 90 degrees by the phase shifter 29, the output of the amplier 38 will bear a plus or minus 90 degrees phase relation to the fixed phase excitation of the motor depending on the direction of the unbalance which drives the modulator 26. Any unbalancevoltage resulting from the received signal not occurring symmetrically with respect to the two gating waves (that is, with respect to the pulses I 85 and |86 contained within the span of the 40o-yard pulse |88) thereby causes rotation of the armature of the motor 28 which is mechanically connected to the variable delay or range unit I to drive a variable condenser forming a part of said unit in one direction or the other. The rotation is in a direction to vary the timing of the output pulse of the range unit in such a way that the gating waves are centered about the received signal |09, reducing the unbalance of the driving voltage to zero. A dial (not shown) on the range unit, calibrated in thousands of yards of range, for example, indicates the'delay introduced by unit I5 and is an accurate indication of the range.

It sometimes happens that in the operation of the range tracking unit described above and its associated apparatus, there is a fading in the received signal so that for periods of time there are no signals from the signal selector. In such a situation there isno diierential current to drive the motor 28 and accordingly the range unit I5 produces a puise I8I the time delay of which with respect to the transmitted pulse |88 is not necessarily an accurate measure of the range. Moreover, it might occasionally happen that the selecting 40o-yard' plus@ los sown in Fig. 4G does not span the desired echo signal which condition may exist in initially setting the apparatus for automatic tracking operation or Y ampliiier 83, the connection fror'n the amplifier to the motor 28 being through the manual contact 32 ofthe control relay 34 and the armature 33 thereof. 'I'he motor 28 is geared or otherwise mechanically connected to the rotary armature of the receiving Selsyn 82. In general, the voltage induced in the receiving Selsyn by the turning of the armature in the sending Selsyn because of the movement of the handwheel 88 is not sunicient to produce a torque large enough to drive the range unit so the ampliiier 83 and motor 28 serve as a torque amplifier for the receiving Selsyn. A suitable servo system involving a sending Selsyn, a receiving Selsyn, a power amplier and motor is disclosed in an application of E. T. Burton, Serial No. 491,789 led June 22, 1943 and which issued as Patent 2,434,259 on January 13, 1948.

In order to operate the control relay 34 from the manual to the automatic position and vice versa, the automatic tracking indicator and control circuit I6 is provided. The circuit I6 is also provided with an indicator to show when the automatic tracking apparatus is following the selected target.

The circuit I6 comprises a 90-degree phase shifter 98 for shifting the phase of the gating waves from the generator 23 by 90 degrees, an amplifier III for these waves, an automatic tracking indicator and control detector 92 (called the A. T. I. C. detector) similar to the double diode tube V4 of Fig. 2, an amplifier 83, an automatic tracking indicator and control relay 94 (called the A. T. I. C. relay) and an automatic tracking indicator 95. Reference will now be made to Fig. 3 for a more detailed description of the apparatus comprising the circuit I6.

Referring now to Fig. 3, gating waves |83 and |84, shown in Fig. 4-D, at the terminals of the secondary winding 55 of the transformer 53 are applied to the two control grids of the double triode tube V5 which .with its associated circuits acts to shift the phase of these two waves by degrees. The two control'grids are connected to ground through resistors I I8 and I I I respectively, and the two cathodes are connected to ground through resistors I I 2 and I I3 respectively. The two plates are connected to the positive terminal of the direct current source 35 through resistor II4. Connected in parallel between the two cathodes of the tube V5 are two series-connected circuits, one comprising the resistor II 5 and the condenser II6 and the other comprising the condenser II'I and the resistor I I8. The tube V5 serves as a double cathode follower tube to drive'the phase shifter, and the outputs of this phase shifter are taken from the points C and D which are the respective common terminals of the two series-connected circuits just described. (If desired the tube V5 can be connected between The voltages applied te the tube v result ln alternating voltages from points A and B to ground which are equal and 180 degrees out -of -phase with' each other. i

voltage between points A and B will be twice that of the yvoltage between either of these points to ground. These voltages are shown in the vector diagram of Fig. 5 by vectors AG. and GB and the voltage AB is 'the sum of these two vectors. In this diagram the point A` is used as a reference point and, therefore, the arrows for vectors AG and BG are not shown 180 degrees apart as would be the case if point G or ground were used asa point of reference. The currents I1 and I: ilowing between points A and B by way of4 parallel paths ACB and ADB, will lead the voltage AB by 45 degrees as shown on the vector diagram since each of these paths has a resistance |5 or H3) in series with a capacitive reactance of the same magnitude at 410 kilocycles (3900 ohms). The voltage drop Em across resistor ll'ii will be' in phase with the current I1 as represented by vector AC. The voltage drop Ecl across condenser ||1 lags behind current Il by 90 degrees and is represented by the vector CB. The voltage drop Ecz across the condenser ||5 lags behind current Iaby 90 degrees and is represented by the vector AD. The voltage drop En: across the resistor |5 is in phase with the current Iz and corresponds to vector DB.

The resulting voltage between C and'D is 90 degrees ahead of the voltage AB. On the vector diagram of Fig. 5 the voltage from point C to ground adds to that from point D to ground so that vectors CG and DG are represented by arrows pointingupwards. However, if point G had been used as the reference point instead of point A, the vector GD would have been shown with the direction of the arrow reversed since the voltage from point C to ground isv 180 degrees out of phase with that from point D to ground.

The vector voltages at points C and D are then r90 degrees ahead of the voltage AB at the cathodes ofthe tube V5 and the voltage to ground at point C is 180 degrees out of phase with the voltage to ground at point D. The voltages from the points C and D are connected to any suitable push-pull amplifier |20.

These voltages are amplied and inverted by the amplifier |20 and applied to the plates of a double diode tube V6 comprising the A. T. I. C1. detector |2i, this double diode tube being similar to the tube V4 shown in Fig. 2. Like the arrangement including the tube V4 in Fig. 2 a signal 'from the signal selector 20 is applied Vto the two plates of the double diode tube V6. The signal from the signal selector 20 applied to' the detector |2| is a positive pulse which raises the voltage of both plates of the double diode by an equal amount. Since the 410-kilocycle gating waves have been shifted `90 degrees in phase by the action of the tube V5 and its associated circuits to become the waves |50 and |5| shown in Fig. 4-I, the right section of the double diode V6, for example, will be conducting during the midele 20o yards of the pulse los while the other 'half of this tube is cut oir. Therefore, a video signal Since this is true, the

` plied tothe tube V1 are equal.

occurringwithin :t100 yards ofthe center of the 40o-yard pulse |08 will cause an additional flow oi' current in one-half of the tube V6 but not in the other half. Fig. 4-J shows the current pulses |52 and 153 through the two halves of the V6 due to the gating waves alone. Fig. 4-K shows the current wave |54 through one diode and Fig. 4L shows the current wave through the other diode when the selected echo |09 is within the middle 200 yards of the 40o-yard pulse |08. However, if the signal occurs within 100 yards of either edge of the 40G-yard range pulse, an additional ow of current will occur in the other diode, that is,- the second or third half sine .wave in the wave |55 in Fig. 4-L will be larger (depending on the rst half of the diode will lremain unchanged.

The voltages in the cathode circuits of the tube V6 are integrated by the condensers connected to them and producepositive signal voltages at the grid of the push-pull direct coupled amplifier |30. It no signal is present within the 40G-yard range interval spanned by the pulse |03, these voltages are equal and the amplied voltages ap- Tube V1 comprises a double triode, the control grids of which receive the output signals of the direct coupled amplifier |30 through resistors T3I and |32. The cathodes are connected together and through a resistor |33 to ground. The control grids are connected to ground through condensers |34 and |35 respectively. The left anode is connected to the positive terminal of the source 45 through resistor |36 while the right anode is connected to the positive terminal of this source through resistors |31 and |36. The coil of the A. T. I. C. relay 94 is connected across the resistor |31, the relay also having an armature |39 and a contact |40. Under this condition the plate current of the tube V1 is made insufficient to operate relay 94. If the signal is within plus or minus 100 yards of the center of the pulse |00, one grid of the tube V1, say for example, the left grid, is driven more negative. Since the cathodes of the tube V1 have a common resistor |33, this reduction of the current in the left cathode will reduce the bias and increase the plate current in the right section of the tube V1.

If the signal from the signal selector 20 is of sufiiy tion of relay 34. Theoperation of the relay 34 causes the armature |42 to make contact with the contact |43 which closes the circuit through the direct current source |44 to cause current to pass through the automatic tracking indicator 95 which may be, for example, a device which gives avisible or an audible indication. The operation of the relay 34 also causes the armature 33 to be moved from a position in contact with the contact element 32 to a position in contact with contact member 3|, or in other words to actuate the armature 33 from the manual to the automatic position. The relation of the contact members 3 I, 32 and 33 to the motor 20 and the amplifier 83 is indicated schematically in Fig. 1. It is obvious that the operation of the A. T. I. C. relay 9,4 can f A1l. be 'used to perform other switching or conditioning operations than those specifically mentioned above. For example, if the radar is one whichhas automatic antenna tracking such as that, for

example, disclosed in the above-identied patent of B. M. Oliver, the energization of this relay maybe used to connect for automatic tracking motors driving the antenna through horizontal.

and vertical angles, while the denergization of the relay 94 may be utilized to condition the circuit for manual operation of these motors in a manner similar to the operation of the motor 28 by the handwheel control 80.

Circuit constants of a radar arrangement in accordance with the invention which has been actually constructed and satisfactorily operated have been indicated on the drawings. It is to be understood, however, that the invention is not limited to the use of elements having these particular circuit constants nor is the invention limited to use in radar systems.

Although the present invention has been ie-l scribed in terms of a preferred illustrative embodiment, it should be realized that the invention and its several features are susceptible of embodiment in a Wide variety of other forms and hence the invention is to be understood as comprehending such other forms as may fairly come within the spirit and letter of the claims.

What is claimed is:

1. In combination, an alternating-current electric motor, separate rst and second means for applying alternating-current energy of the same frequency to said motor to cause variations in the output thereof, the lrst of said energy-applying means including a manually-controlled servosystem mechanically connected to the motor, circuit control means, means for applying to Said circuit control means a series of time spaced pulses, each of said pulses having a durationl shorter than that of a half cycle of a sinusoidal wave of the frequency of the alternating current applied to said motor, means including a relay for normally connecting said motor to said second energy applying means during the time said pulses are being applied to said circuit control means, and means, including said relay, responsive to the failure of rsaid pulses for disconnecting said second energy applying means from said motor and connecting the first of said energy applying means thereto.

2. I n combination, an alternating-current electric motor, separate first and second means for applying alternating-current energy of the same frequency to said motor to cause variations in the output thereof, the first of said energy-applying means including a manually-controlled servosystem connected to the motor, circuit control means, means for applying to said circuit control means a series of time spaced pulses, each of said pulses having a duration shorter than that of a half cycle of a sinusoidal wave of the frequency oi the alternating current applied to said motor, means including a relay for normally connecting said motor to said second energy applying means during the time said pulses are being applied to said circuit control means, and means, including said relay, responsive to the failure of said pulses for .disconnecting said second energy applying means from said motor and connecting the first of said energy applying means thereto.

BERNARD M. OLIVER.

REFERENCES CITED The following references are of record in the file of this patent?-l UNITED STATES PATENTS A 

